This present invention relates to a method and a device for controlling a DC servomotor for driving a rotating load such as a valve.
When a rotating load such as a valve is driven by a motor, a rotating load driving device using a DC servomotor as a driving source is often used.
A valve being controlled to open and close according to various control conditions is often used in order to adjust characteristics of various machines and control operations of the machines. For example, in a two-cycle combustion engine, a valve for adjusting timing of exhaust in order to improve output characteristics of the engine and to purify exhaust gas of the engine, a valve for opening and closing a cavity connected to an exhaust pipe to adjust a resonance frequency of the exhaust pipe in order to improve exhaust efficiency and a valve for adjusting air-intake timing are provided as needed. These valves are controlled according to various control conditions such as a rotational speed and an opening degree of a throttle valve.
As a device for driving a valve provided in a combustion engine, a device is used which is provided with a DC servomotor, a driven member to be driven by the DC servomotor, an operation member attached to an operation shaft of the valve in order to rotationally operate the valve and a wire for coupling the driven member and the operation member.
In this kind of driving device, with the rotation of the driven member to be driven by the motor, the operation member is rotated while being pulled by the wire, and the operation shaft of the valve is rotationally operated by the rotation of the operation member.
If the valve is driven by such a driving device, a driving current is supplied to the motor at a duty ratio of 100% at the start of control to cause the valve to carry out an operation of moving a valve body of the valve from one limit position (e.g., fully closed position) to the other limit position (e.g., fully opened position) and an operation of moving the valve body from the other limit position (e.g., fully opened position) to one limit position (e.g., fully closed position). In this way, self-cleaning of the valve is performed. Foreign matters such as carbon and dusts adhered to a movable portion of the valve are removed by this self-cleaning operation to allow the valve to move smoothly in subsequent control operations.
In addition, when this self-cleaning operation is performed, a stop position of the driven member at the point when the valve body of the valve stops by reaching the fully closed position and a stop position of the driven member at the point when the valve body of the valve stops by reaching the fully opened position are detected and stored as a fully-opened-side final stop position and a fully-closed-side final stop position of the driven member, respectively.
During the operation of the combustion engine, a position of the driven member attached to the output shaft of the motor is detected by a position detector such as a potentiometer. Then, a duty ratio of a driving current of the motor is controlled such that a deviation between the detected current position of the driven member and a target position of the driven member corresponding to an optimal position of the valve body of the valve, which is determined by various control conditions such as a rotational speed of the engine and an opening degree of the throttle valve, becomes zero. In this way, the position of the valve body of the valve (hereinafter referred to simply as the position of the valve) is coincided with the optimal position.
As described above, the valve driving device is comprised such that the driven member that is driven by the motor and the operation member attached to the operation shaft of the valve are coupled by a wire and the valve is driven while the operation member is pulled via the wire with the rotation of the driven member. In the valve driving device, when a driving current with a duty ratio of 100% is supplied to the motor and the operation shaft of the valve is driven toward the limit position (the fully opened position or the fully closed position), even after the operation shaft of the valve reaches the limit position, the driven member is displaced to a certain degree by the extension of the wire due to a large output torque of the motor caused by the driving current with a duty ratio of 100%. Thus, the final stop position of the driven member and the limit position of the operation shaft of the valve cannot accurately correspond to each other. Therefore, in the conventional device, a position that is beyond the position of the driven member corresponding to the limit position of the operation shaft of the valve may be detected as the final stop position of the driven member.
However, during the operation of the engine, when the driven member is controlled to reach the final stop position with the target position of the driven member as the final stop position in order to displace the operation shaft of the valve to the limit position, it is not possible to always flow the driving current with a duty ratio of 100% in order to have good controllability. As the position of the driven member is approaching the final stop position, it is necessary to reduce the duty ratio of the driving current. Thus, when the operation shaft of the valve reaches the limit position and stops, the motor also stops. Therefore, if the final stop position of the driven member detected when the control is started is a position that is beyond a position corresponding to the limit position of the operation shaft of the valve, the motor stops and is locked in the state in which the driven member cannot be displaced to the final stop position. If the motor continues to be locked, since the driving current continues to flow into an armature coil while the motor is stopped, it is likely that a coil of the motor is burned and a switch element of a circuit for controlling the driving current of the motor is damaged. Thus, it is necessary to provide means for detecting that the motor is locked and immediately block the driving current of the motor when it is detected by this means that the motor is locked. However, since it requires a certain period of time to detect that the motor is locked, protection of the motor and protection of the circuit for controlling the motor cannot be accurately realized.
In addition, in the case in which the final stop position of the driven member is shifted from the position corresponding to the limit position of the operation shaft of the valve at the start of the control, if the driving current of the motor is blocked when the operation shaft of the valve reaches the limit position and the motor stops, the driven member may be pulled back by tension of the wire. If the driven member is pulled back in this way, since the operation shaft of the valve may also be pulled back from the limit position, the control for causing the operation shaft of the valve to reach the limit position cannot be accurately performed.
As described above, in the driving device in which the driven member attached to the motor side and the operation member attached to the valve side are coupled by the wire, it may be difficult to accurately correspond the final stop position of the driven member to the limit position of the operation member due to extension of the wire. Thus, the control for displacing the operation shaft of the valve to the limit position cannot be accurately performed.
Further, although a load of the driving device is assumed to be a valve in the above-mentioned example, the same problem occurs in the case in which a driven member to be driven by a DC servomotor and an operation member for operating a rotating load other than a valve are coupled by a wire to control the DC servomotor, thereby controlling a stop position of the load.
Accordingly, it is an object of the present invention to provide a control method and a control device for a DC servomotor for driving a load, which, when a driven member to be driven by a DC servomotor and an operation member for operating a load such as a valve are coupled by a wire to rotate the load, can accurately detect a final stop position of the driven member corresponding to a limit position of the load to control a position of the load accurately while preventing the situation in which power supply to the motor cannot be stopped and the motor to be excessively heated when the load reaches the limit position.
According to an aspect of the present invention, there is provided a method of controlling a DC servomotor of a rotating load driving device comprising: the DC servomotor for driving a rotating load; a driven member to be driven and rotated by the DC servomotor; an operation member attached to an operation shaft of a rotating load, a rotational range of which is mechanically limited; and a wire for coupling the operation member and the driven member, and rotating the operation member with the rotation of the driven member while pulling the operation member by the wire to rotate the rotating load. In the present invention, after carrying out a motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the rotating load toward a limit position; and a driving current attenuating step of gradually attenuating the driving current to be finally zero after the motor stops in the motor driving step, and detecting a rotational position of the driven member at the point when the driving current becomes zero in the driving current attenuating step as a final step position of the driven member, the method controls the driving current of the motor to bring a deviation between a target position of the driven member corresponding to a target position of the rotating load and a current position of the driven member to zero while keeping the position of the driven member not to be beyond the final stop position.
As described above, when a large current is flown to the motor to rotate the rotating load toward the limit position, the driven member stops in a position where a tension of the wire and a driving torque of the motor balance with each other after the rotating load reaches the limit position and stops. When the driving current is gradually attenuated in this state, the driven member is pulled back slowly by the tension of the wire and, when the driving current becomes zero, reaches an original final stop position corresponding to the limit position of the rotating load. Therefore, when comprised as described above, the method can accurately detect the final stop position of the driven member corresponding to the limit position of the rotating load and accurately carry out subsequent controls.
In addition, when comprised as described above, since it is possible to correspond the final stop position of the driven member to the limit position of the rotating load, the method can immediately detect that the driven member has reached the limit position to stop the motor when the rotating load has reached the limit position and stopped, and the method can prevent the motor from being excessively heated due to the delay in detecting that the motor has stopped.
According to another aspect of the present invention, there is provided a method of controlling a DC servomotor of a valve driving device comprising: the DC servomotor; a driven member to be driven by the DC servomotor and rotated in one direction and in the other direction following the rotation of the motor in one direction and in the other direction; an operation member attached to an operation shaft of a valve, a rotational range of which is mechanically limited such that the operation shaft rotates between a fully-closed-side limit position and a fully-opened-side limit position; and first and second wires provided so as to couple the driven member and the operation member, and rotating the operation shaft of the valve toward the fully-opened-side limit position while pulling the operation member by the first wire when the driven member rotates in one direction and rotates the operation shaft of the valve toward the fully-closed-side limit position while pulling the operation member by the second wire when the driven member rotates in the other direction. In the present invention, after carrying out a fully-opened-side final position detecting step for carrying out a first motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the operation shaft of the valve toward the fully-opened-side limit position; and a first driving current attenuating step of gradually attenuating the driving current to be finally zero after the motor stops in the first motor driving step, to detect a rotational position of the driven member at the point when the driving current becomes zero in the first driving current attenuating step as the fully-opened-side final stop position of the driven member and, a fully-closed-side final position detecting step for carrying out a second motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the operation shaft of the valve toward the fully-closed-side limit position; and a second driving current attenuating step of gradually attenuating the driving current to be finally zero after the motor stops in the second motor driving step, to detect a rotational position of the driven member at the point when the driving current becomes zero in the second driving current attenuating step as the fully-closed-side final stop position of the driven member, the method controls the driving current of the motor to bring a deviation between a target position of the driven member set between the fully-opened-side final stop position and the fully-closed-side final stop position and a current position of the driven member to zero.
The above-mentioned valve is, for example, a valve for adjusting a characteristic of a combustion engine such as an exhaust valve to be provided for adjusting exhaust timing of a two-cycle combustion engine and a valve for opening and closing a cavity connected to an exhaust pipe in order to adjust a resonance frequency of an exhaust pipe of a combustion engine.
According to another aspect of the present invention, a control device of a DC servomotor for driving a rotating load is provided, which comprises:
a driving mechanism that includes a DC servomotor; a driven member to be driven and rotated by the DC servomotor; an operation member attached to an operation shaft of a rotating load, a rotational range of which is mechanically limited; and a wire connecting the operation member and the driving member, and rotates the operation member while pulling the operation member by the wire following the rotation of the driving member to drive the rotating load;
final stop position detecting means for carrying out a motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the rotating load toward a limit position and a driving current attenuating step of gradually attenuating a driving current after the motor stops in the motor driving step to finally bring the driving current to zero to detect a rotational position of the driven member at the point when the driving current becomes zero in the driving current attenuating step as a final stop position of the driven member; and
motor driving current controlling means for controlling a driving current of the motor to bring a deviation between a target position of the driven member corresponding to a target position of the rotating load and a current position of the driven member to zero while keeping the position of the driven member not to be beyond the final stop position.
According to yet another aspect of the present invention, a control device of a DC servomotor for driving a valve is provided, which comprises:
a driving mechanism that includes a DC servomotor; a driven member to be driven by the DC servomotor and rotated in one direction and in the other direction following the rotation of the motor in one direction and in the other direction; an operation member attached to an operation shaft of a valve, a rotational range of which is mechanically limited such that the operation shaft rotates between a fully-closed-side limit position and a fully-opened-side limit position; and first and second wires provided so as to couple the driven member and the operation member, and the valve driving mechanism rotates the operation shaft of the valve toward the fully-opened-side limit position while pulling the operation member by the first wire when the driven member rotates in one direction and rotates the operation shaft of the valve to toward the fully-closed-side limit position while pulling the operation member by the second wire when the driven member rotates in the other direction;
fully-opened-side final stop position detecting means for carrying out a first motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the operation shaft of the valve toward the fully-opened-side limit position and a first driving current attenuating step of gradually attenuating the driving current to be finally zero after the motor stops in the first motor driving step to detect a rotational position of the driven member at the point when the driving current becomes zero in the first driving current attenuating step as the fully-opened-side final stop position of the driven member;
fully-closed-side final stop position detecting means for carrying out a second motor driving step of driving a motor such that a sufficiently large driving current is flown to the motor to rotate the operation shaft of the valve toward the fully-closed-side limit position and a second driving current attenuating step of gradually attenuating the driving current to be finally zero after the motor stops in the second motor driving step to detect a rotational position of the driven member at the point when the driving current becomes zero in the second driving current attenuating step as the fully-closed-side final stop position of the driven member; and
motor driving current controlling means for controlling the driving current of the motor to bring a deviation between a target position of the driven member set between the fully-opened-side final stop position and the fully-closed-side final stop position and a current position of the driven member to zero.